A technique is well known in which a capillary device incorporating a combination of a plurality of capillaries is used for supplying and running an electrophoresis medium together with a sample to be analyzed or separated to utilize a target sample for separation and analysis. In addition, a technique where a sample such as fluorescence-labeled DNA or protein is supplied to a capillary is described, for example, in U.S. Pat. Nos. 5,366,608, 5,529,679, 5,516,409, 5,730,850, 5,790,727, 5,582,705, 5,439,578 and 5,274,240. In view of the throughput for separation and analysis, use of multi-capillaries is more advantageous than an electrophoresis method employing a flat gel. Japanese Patent Laid-Open Application No. 9-96623 describes a capillary array electrophoresis apparatus.
FIG. 2 is a perspective view for illustrating a capillary array device. Each of capillaries 1 has an outer diameter of 0.1 to 0.7 mm and an inner diameter of 0.02 to 0.5 mm, and is coated with a polyimide resin. The capillary array device is formed with an arrangement of a plurality (generally, several to several-tens) of capillaries which are quartz pipes. The capillary array device is further provided with a load header 4 for drawing fluorescence-labeled DNA samples or the like from sample reservoirs into the respective capillaries by electrophoresis, a separator 16 for aligning the plurality of capillaries, a detector (window unit) 5 for firmly holding the capillaries 1 in the order of the sample numbers at the load header 4, and a capillary head 17 for bundling and holding the plurality of capillaries together. The load header 4 is provided with hollow electrodes 20 for applying an electrophoresis voltage to the capillaries. The detector (window unit) 5 is provided with an aperture for irradiating the arrangement of capillaries and an aperture from which the light from the capillaries comes out. According to the present invention, the detector 5 can be any detector as long as parts of the plurality of capillaries to be irradiated with laser light (parts of the capillaries where they allow transmission of the laser light for exciting the sample) can be held in parallel.
FIG. 3 is a schematic view showing an electrophoresis system. The sample inlet ends of the capillaries 1 and the hollow electrodes 20, which are protruding from the load header 4 of the capillary array device shown in FIG. 2 are immersed into a sample tray 3 which includes a plurality of sample reservoirs 2 each containing a fluorescence-labeled DNA sample. The other ends of the capillaries 1 at the capillary head 17 are attached to a buffer reservoir 14 containing a buffer 13 by pressure-proof sealing. A high voltage of about 15 kV from a high-voltage power source 15 is applied to the buffer reservoir 14 and the load header 4, whereby the samples in the sample reservoirs are subjected to electrophoresis for sample separation with the buffer 13 from the buffer reservoir 14 supplied into the capillaries 1.
A laser light source 6 radiates excitation light to the detector (window unit) 5 via an excitation optical system including mirrors 7, a beam splitter 8, convergence lenses 9 and the like. The excitation light irradiation allows fluorescence 10 as signal light output from the samples running through the capillaries 1 to be detected by a CCD camera 12 via a detection lens system 11. The detected signal is processed by a signal processing unit 21.
In the exemplary electrophoresis system shown in the figure, laser light is radiated to both sides of the capillary array device containing DNA or proteins to be electrophoresed. The laser light is converged by means of lens function of the capillaries so that all of the capillaries are irradiated with the excitation light, whereby fluorescence from each capillary is detected by the detection optical system.
The load header 4 samples the samples and also serves as the hollow electrodes 20 on the sample reservoir side for applying a high voltage between the samples and the buffer reservoir 14. FIGS. 4A and 4B are schematic views showing a structure of a conventional load header. Sixteen capillaries 1 are each inserted into the respective hollow electrodes 20 made of narrow stainless steel (hereinafter, simply referred to as “SUS”) pipes, and fixed with an epoxy adhesive 27. The sample side ends of the capillaries 1 are slightly protruding from the hollow electrodes 20. As shown in FIGS. 5A and 5B, the sixteen hollow electrodes 20 are arranged on a holding frame 22, aligned with a connection plate 23 with a strict margin, and are bonded to the connection plate 23 with solder 24. SUS pipe electrodes are used because the samples or reagents to be separated and analyzed are corrosive.
The bonded hollow electrodes 20 and the connection plate 23 are incorporated into a plastic holder 25. A lid 26 is fixed onto the holder 25 by ultrasonic bonding. Then, the holder 25 and the hollow electrodes 20 are sealed and fixed from outside with an adhesive 27, thereby achieving a complete load header. The capillaries 1 are sealed in the lid 26 by the adhesive 27 so as to prevent them from slipping out and to avoid high voltage leak. The connection plate 23 is partially bent by 90° so as to allow connection to a high-voltage contact (not shown) via the aperture in the holder 25.
The capillary array device is an expendable item that looses desirable characteristics after being used for several-tens of times.
The above-described conventional load header has the following problems.
(1) Load header assembly requires a number of operations such as adhesion and bonding, which requires time and results in production at a high cost.
(2) Operations such as adhesion and bonding requires skill of the operator, and are sensitive to operation conditions and environment, which results in poor reliability.
(3) Since a strong acid soldering flux is used for soldering the connection plate and the SUS electrodes, the flux becomes ionic impurities, thereby deteriorating electrophoresis. Therefore, the narrow electrodes need to be washed both inside and outside by high-quality washing.